The invention relates to a fixing agent in the form of an oil/water type, lamellar emulsion or suspension, which fixing agent can be used for fixing a fertilizer powder to the surfaces of plant seeds. The invention also relates to a method for preparing such a fixing agent.
The rapidity with which the roots of a plant reach the fertilizer has great significance for the ability of the plant to take up the nutrients present in the fertilizer and for the success of the initial development and growth of the plant in the first three weeks.
The quantities of the principal nutrients (N, K, P, Ca, S, Mg) passing from fertilizers into plants, i.e. the efficiency of the nutrients, usually vary from a few percent to 70-80 percent. The efficiency of phosphorus in particular is low, approx. 5-20%. The efficiencies of trace elements (B, Co, Cu, Fe, Mn, Mo, Zn, Cl) are often even lower than this.
The method by which the fertilizer is spread, i.e. how far from the seed the fertilizer is deposited, affects the ability of the plant to utilize the nutrients. The nutrients in a fertilizer deposited far from the seed, for example at a distance of 6 cm from it, may have time to react with soil minerals and to form poorly soluble compounds even before the roots of the plant have reached the location of the fertilizer.
When, for example, phosphorus fertilization is carried out, as described above, by conventional broadcasting of the fertilizer on the soil surface or by mixing it into the surface layer of the soil, the phosphorus efficiency is 5-10%. If the fertilizer is spread by row application or tape application at a specified distance from the seed, the phosphorus efficiency is approx. 10%.
A somewhat better phosphorus efficiency is achieved when the phosphorus fertilizer is deposited in the immediate vicinity of the seed or when the seed is coated with the fertilizer. In this case the efficiencies are, respectively, 15% and 20%.
The coating of plant seeds for various reasons has long been a known technology. There are different surface treatments, beginning from the simple and conventional seed dressing with biocides to combat plant diseases and noxious insects. In this case the seeds as such are treated with a fine-ground active agent or a powder mixture containing it, or the active agent is dissolved or slurried in a suitable solvent, often water or an organic solvent, and the seeds are then treated with the obtained solution or slurry.
From patent publication U.S. Pat. No. 4,761,423 there is known a wet seed dressing method wherein the seeds are impregnated with an emulsion that contains water, oil, an emulsifier and a biocide.
Coating of seeds has also been used for delaying the germination of seeds. Polymers have been used as fixing agents also in the coating of seeds with substances having other effects. Coating may, for example, improve the ability of the seeds to withstand drought, heat, soil salinity, or other external stress factors.
With the help of coating, for example, lightweight seeds of rice can be rendered heavier, whereupon they will not be so easily carried by water or wind; see, for example, patent publication U.S. Pat. No. 4,192,095.
It is also generally known to add nutrients to a coating in order to promote plant growth.
Grass seeds have been treated with, for example, lime or talc in order to ensure the establishment of a lawn (Scott 1975). The coating of seeds with nutrients is discussed in several studies (e.g. Heydecker and Coolbear 1977, Rebafka et al. 1983, Scott et al. 1987). The greatest problems have been a poor germination percentage of the seeds, especially when oil has been used as the fixing agent, and poor attachment of nutrients to the seed surface when aqueous solutions have been used.
A great deal of research has been conducted in order to solve these problems. Various fixing agent compositions have been experimented with for the fixing of nutrients or other growth-promoting substances or compositions to the surfaces of plant seeds.
In particular, the usability of various polymers has been experimented with. It is, for example, a known method to coat seeds with water-soluble polymers such as starch, methyl cellulose and gum arabic. The greatest disadvantage is the large amount of water associated with the use of these polymers. The handling of a large amount of water requires special apparatus, and the coating process is slow. In order to prevent the wetting of the seeds, the seeds must often be dried at a low temperature. The above-mentioned polymers often form a hard, easily breaking coat around the seeds.
Patent publication WO 9325078 describes a composition used for the coating of seeds, which composition contains a polysaccharide hydrolysate, for example, carboxymethyl cellulose or carboxymethyl starch hydroxylate. The aqueous solutions of these may also be sprayed in the form of relatively concentrated aqueous solutions (30%) onto the seed surfaces.
The use of water-insoluble polymers, on the other hand, usually requires the use of an organic solvent, in which case a large solvent amount may promote the penetration of the polymer into the seed. It is also possible to use aqueous suspensions of these polymers for the treatment of seeds. For example, CA PLUS 112:17756 (PL 146138) and CA PLUS 122:49097 (PL 159474) describe such an application.
Patent publication U.S. Pat. No. 4,251,952 describes seeds coated with a mixture of a water-insoluble polymer and sugar. The polymers used are various commercial poly- or copolymers.
From unpublished patent application FI 19992768 (Kemira Agro Oy) there is known a composition intended for the surface treatment of seeds, the composition comprising a fixing agent layer made up of an oil/water emulsion and a layer of fertilizer powder. The fixing agent mixture used for forming the fixing agent layer may also contain a fluid byproduct of agriculture or fermentation.
In addition to the disadvantages already stated above, the prior-known methods may also have the disadvantage of stickiness of the coated seed surfaces, causing the seeds to stick together and giving the seeds poor flow properties. The apparatus required for the handling of the seeds also becomes easily soiled. A coating too moist, for its part, may cause premature germination of the seeds. The prior-known methods also have the disadvantage of incomplete or non-uniform adhesion of the active agent to the seeds and/or its poor retention on seed surfaces.